Microbiota dysbiosis and mucosal hyperinnervation contribute to intestinal hyperalgesia in a mouse model of post-infectious irritable bowel syndrome

Post-infectious irritable bowel syndrome (PI-IBS) is defined by persistent gastrointestinal symptoms that follow recovery from an episode of infectious enteritis, which worsen after experiencing psychological stress. Mucosal neurite outgrowth stimulated by neurotrophins and serotonin/5-hydroxytryptamine receptor subtype 7 (5-HT ₇ ) activation is linked to visceral hypersensitivity. Rifaximin (RFX) is a poorly absorbed antibiotic that improves IBS symptoms; however, the exact mechanisms remain unclear. The aims are to evaluate changes in microbiota and neuroplasticity in PI-IBS mice after RFX treatment, and the analgesic effects of combined treatment with a novel 5-HT ₇ antagonist CYY1005 (CYY). A mouse model with dual triggers of Giardia postinfection and water avoidance stress exhibited intestinal hyperalgesia, as measured by visceromotor responses (VMRs). Higher Shannon diversity and increased relative abundances of Lachnospiraceae, Deholobactericeae, and Ruminococcus gnavus were observed in the microbiota of PI-IBS mice, which were restored to baseline after RFX treatment. Reduced VMRs were associated with attenuated mucosal neurite outgrowth and brain-derived neurotrophic factor (BDNF) expression after RFX treatment. BDNF/TrkB activation induced mTOR-dependent nerve fiber elongation and upregulated tryptophan hydroxylase 2 and 5-HT ₇ expression via Rac1/ROCK pathway in SH-SY5Y neuron cultures. Combined treatment with RFX and CYY reduced VMRs to levels comparable to those of the control groups. Lastly, bacteria-free colonic mouse supernatants induced neurite elongation in SH-SY5Y cells, which was inhibited by neutralizing anti-BDNF antibodies. In conclusion, microbiota restoration by RFX treatment attenuated BDNF-induced neurite outgrowth and alleviated visceral hypersensitivity in mice. Analgesic combinations of RFX and a 5-HT ₇ receptor antagonist reduced intestinal nociception to baseline levels.